Interlaced vibrating electrode

ABSTRACT

AN APPARATUS FOR DEVELOPING A LATENT ELECTROSTATIC IMAGE WHEREIN THE DEVELOPER MATERIAL IS CIRCULATED IN A HIGHLY MOBILE MANNER PAST THE IMAGE BEARING SURFACE. THE HIGH MOBILITY OF THE DEVELOPER IS ACHIEVED BY THE USE OF INTERLACED VIBRATING ELECTRODE MEMBERS WHEREIN THE RELATIVE MOVEMENT THEREOF CAUSES DEVELOPER MATERIAL TO BE CIRCULATED ABOUT AN INNER ELECTRODE MEANS THEREBY ACHIEVING A HIGH DEGREE OF CIRCULATION OF THE CARRIER MATERIAL IN THE DEVELOPER. THE HIGH DEGREE OF CIRCULATION OF THE CARRIER PARTICLES ALLEVIATES THE PROBLEM OF STICKING OF THE CARRIER MATERIAL TO THE IMAGE BEARING SURFACE AND OVERCOMES INSUFFICIENT LEADING EDGE DEVELOPMENT OF SOLID IMAGE AREAS.

Nov. 23, 1971 D. J. DONALIES 3,621,816

INTERLACED VIBRATING ELECTRODE Filed Oct. 29, 1969 3 Sheets-Sheet l INVENTOR. DANIEL J. DONALIES BY 9M% 9% ATTORNEY Nov. 23, 1971 D. J. DONALIES 3,621,816

INTERLACED VIBRAT ING ELECTRODE- Filed Oct. 29, 1969 I) Sh00ts-$h0ot 2 Nov. 1971 D. J. DONALIES 3 INTERLACED VIBRATING ELECTRODE Filed Oct. 29 1969 3 Sheets-Sheet 5 United States Patent Office 3,621,816 Patented Nov. 23, 1971 US. Cl. 118-637 9 Claims ABSTRACT OF THE DISCLOSURE An apparatus for developing a latent electrostatic image wherein the developer material is circulated in a highly mobile manner past the image bearing surface. The high mobility of the developer is achieved by the use of interlaced vibrating electrode members wherein the relative movement thereof causes developer material to be circulated about an inner electrode means thereby achieving a high degree of circulation of the carrier material in the developer. The high degree of circulation of the carrier particles alleviates the problem of sticking of the carrier material to the image bearing surface and overcomes insufficient leading edge development of solid image areas.

BACKGROUND OF THE INVENTION This invention relates in general to developing a latent electrostatic image and, in particular, to an apparatus for circulating developer material in a highly mobile state past a photosensitive surface supporting a latent electrostatic image to be developed.

More specifically, this invention relates to a development apparatus wherein relative movement between interlaced electrode members effects a circulation of developer material about an inner member in a highly fluidized state. The developer circulation about the inner electrode creates a degree of mobility of the developer to achieve a high degree of intermixing of the carrier material and alleviate the problem of sticking of the carrier particle to the photosensitive surface and improve the development of the leading edge of solid area images.

In the process of xerography, a xerographic plate comprising a layer of photoconductive material and a conductive backing is given a uniform electric charge on the surface and then is exposed to the subject matter to be reproduced by various projection techniques. This exposure discharges the plate in accordance with the light intensity reaching it thereby creating a latent electrostatic image on or in the plate. Development of the image is effected by developers which may comprise in general a mixture of suitable, pigmented or dyed, resin powder, hereinafter referred to as toner, which is brought into contact with the plate by various well-known development techniques. During such development of the image, the toner powder is brought into surface contact with a photoconductive coating and is held there electrostatically in a pattern corresponding to the latent electrostatic image. Thereafter, the developed xerographic image may be transferred to a support material to which it may be fixed by any suitable means such as heat fusing.

Various development devices have been utilized in xerography to develop a latent electrostatic image formed on a photosensitive surface One well known technique of development is desclosed in US. Pat. No. 2,573,881 to Walkup et al., wherein toner carried by carrier particles is rolled or cascaded over the latent electrostatic image bearing surface. The carrier and toner materials are selected so that a triboelectric attraction exists between them causing the two particles to cling together and acquire an opposite charge. In practice, each carrier has numerous toner particles attracted thereon allowing them to be transferred into contact with the photoconductive surface wherein the greater electrostatic attraction of the latent image will overcome the triboelectric attraction between the two developer components causing toner to be stripped off the carrier and electrostatically bonded to the charged image to effect development thereof.

Several difiiculities are associated with the aforementioned cascade method of development. Cascade development, for example, presents a problem in developing large image areas, since the electrostatic field of the image is stronger at the edges than in the central portion the image toner is not attracted to the image since the field is not strong enough to overcome the triboelectric attraction between the two components of the developer. Such a phenomenon will result in incomplete development of the central portion of an image while the edges are comparatively better developed.

Cascade development also requires a thorough intermixing of developer after repeated development. If intermixing does not occur, a defect in development referred to as image striations result because of localized carrier material becoming depleted of toner powder. Normally, toner depletition occurs in cascade development when the carrier and toner materials move past the'image in one direction across the photosensitive surface. Since images normally have varying size latent charge patterns to be developed along the direction of flow, repeated development causes the developer flow moving past the more massive image areas to be depleted of toner in a greater amount than the less massive areas thereby causing certain areas of the developer flow to be depleted of toner more than others. Therefore, elaborate inter-mixing systems are required to overcome this toner depletion problem.

Further, in cascade development the carrier particles in the cascade developer flow often stick or bead to the image bearing surface whereupon the beading carriers become depleted of toner material while underneath levels of developer not in direct contact with the image retain sufficient toner to produce effective development. The effect of beading of the carriers produces a masking of the image surface to prevent better tonerized materials from contacting the image. Such beading is caused by the fact that developer flow is not sufficiently turbulent in the cascade development to achieve inter-mixing between carrier beads in contact with the image and the carriers in the underneath levels of the flow.

One attempt in the prior art to overcome some of the aforementioned problems presented by the cascade technique of development has been by eifecting turbulence of the developer flow as it passes the image bearing surface. An example of such a fluidizing of developer flow is disclosed in the US. Pat. No. 3,357,399 to Fisher wherein a two component developer is cascaded past the image bearing surface and is agitated into a fluidized state in the development zone. The fluidizing of developer results in retoning of the carrier particles in contact with the image by effecting transfer of toner from underlayers of the flow to the toner depleted carrier in contact with the image. Also, the turbulence of the flow causes some of the carrier particles not in direct contact with photosensitive surface to be interchanged with the carrier particles in contact therewith to further insure that sufiiciently tonerized carriers are adjacent the image.

Fluidized developer is also found to increase development contact with the image and alleviates streaking thereof to enhance development as compared to the cascade method. However, prior art fluidizing and cascade development devices do not adequately develop the leading edge of solid image areas on a photosensitive surface wherein leading edge refers to the first portion or edge of a solid area that is contacted by the developer flow. Such a development deficiency is related to the degree of intermixing of carrier particles from the underlayers of the developer flow and to the insuflicient retoning of carrier actually contacting the image bearing surface. If carrier beads become depleted of toner, the attractive force required to strip toner therefrom increases to thereby increase the time necessary for the field of the image actually to attract toner. Since the charge pattern on the surface moves relative to the developer, a greater area of the leading edge thereof is thus traversed without development if the response time is increased. Therefore, if adequately tonerized beads are presented in contact with the image, significantly improved leading edge development results.

Even though the prior art fluidizing devices improve the circulation of carrier particles as compared to the cascade techniques, the prior art development devices which fluidize the developer material are relatively inefficient in creating the desired degree of turbulence necessary to prevent the masking of toner depleted developer upon the image bearing surface. Also, since the movement of the developer material in the development zone is greatly dependent on the relative motion of the image bearing surface, the masking of localized developer material on the photosensitive surface is aggravated by the inherent frictional coupling therebetween. Therefore, it is desirable in Xerography to provide an appaartus for developing latent electrostatic images which provides the de gree of mobility of the developer material sufficient to insure that adequately tonerized carriers are circulated past the image bearing surface to prevent bead sticking and insufiicient development of the leading edge of solid area images.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to develop a latent electrostatic image with an improved apparatus.

Another object of this invention is to improve the development of the leading edge of a latent electrostatic image.

A further object of this invention is to eliminate sticking of the carrier particles to the image bearing surface during development.

Still another object of this invention is to increase the turbulence and circulation of adequately tonerized carrier particles past the latent electrostatic image to be developed.

These and other objects are attained in accordance with the present invention wherein there is provided an effective development device which overcomes many of the aforementioned difiiculties presented by the prior art development systems. The invention comprises a fluidizing development device wherein a plurality of interlaced vaned type electrodes are given a relative motion to cause a flow of developer material around an inner electrode adjacent a surface bearing an image to be developed. In one embodiment of the invention, flow of developer material circulates about the inner electrode in a helical manner to provide high mobility of the developer flow and prevent masking and adherence of localized carrier material to the photosensitive surface. Similarly, in another embodiment, disclosed herein, optimumly tonerized carrier is orbited about the inner vane to also achieve a high degree of turbulence.

The mobile circulation around the electrode member in the present invention is produced by positioning an electrode member within two channel members angularly oriented thereto. The electrode member is relatively oscillated therein to move against one adjacent channel member in one direction and move against the other channel member in the opposite direction. Because of the angular orientation of the respective adjacent channel members, the motion of the electrode member toward one channel member imposes a force component on the developer therebetween to move the material in a first direction and the motion of the electrode toward the other channel member imposes a motion of the developer material in an opposite second direction. Therefore, the developer material tends to move up the electrode member on one side thereof and down the other side as the electrode member is oscillated within the channel members. Accordingly, an orbiting or circulation of the developer around the electrode member is achieved to provide a high degree of mobility of the material relative to the image bearing surface.

The vane member and channel members according to one form of the present invention are oriented to extend along the direction of movement of the photosensitive surface to produce a helical motion of the developer along the vane members wherein the helical motion may be increased or modified by elevating one end of the vane member. Alternatively, the vane member and the channel members of the invention may be oriented without substantially extending in the direction of motion of the sur face and produce an orbiting flow of developer whereupon the carrier may be tonerized by a sump located beneath the vane members.

In both forms of motion of the developer material utilized in the present invention, a high level of circulation of adequately tonerized carrier is achieved past the image areas to effect more efiicient development of the leading edge of solid areas as produced by prior art development devices. Further, the circulatory motion of the developer achieves a degree of turbulence of the material to overcome the problem of heading of the carrier particles to the image bearing surface as encountered in the use of prior art cascade and fluidized development systems.

DESCRIPTION OF THE DRAWINGS Further objects of this invention together with additional features contributing thereto and advantages accruing therefrom will be apparent from the following description of several embodiments of the invention when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic illustration of the drum type xerographic machine utilizing the development device of the present invention;

FIG. 2 is a schematic side view of one embodiment of the development apparatus of the present invention;

FIG. 3 is a top schematic view of the development device illustrated in FIG. 2 of the present invention;

FIG. 4 is a schematic end view of the development device taken along line 44 in FIG. 3 device according to the present invention; and

FIG. 5 is a schematic illustration of a Second embodiment of the development device of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there is shown :1 schematic view of a drum type xerographic machine utilizing the develop ment device of the present invention. The central element of the machine is a drum 1 mounted for rotation by suitaable means and drivable in a conventional direction by a motor. The drum 1 comprises an outer surface with a layer of photoconductive insulating material such as vitreous selenium or other suitable surface. A uniform electric charge is placed on the photoconductive surface of the drum by means of a conventional corona charging device 2. The uniformly charged surface is then moved to an exposure means 3 which may be any well-known device which will expose the charged surface to copy to be reproduced and form a latent electrostatic image of the copy on the photosensitive surface.

Following the formation of a latent electrostatic image of a copy, the image on the drum will move to the development device 10 according to the present invention (to be described in detail later) to bring the latent electrostatic image in contact with developing material comprising, for example, carrier particles and electroscopic toner, for development thereof. After development, the visible image moves to a transfer means 4 and is transferred from the drum to a web 5 of paper or the like which is positioned in contact with the drum by roller 6. A second corona charging device 7 applies a charge to the back of the web 5 to facilitate transfer of the toner powder in image form. The toner image on the Web then moves past the heating element 8 which permanently affixes the toner to the paper web to form a duplicate of the original copy. A rotating brush 9 contacts the belt surface after it moves past the transfer device to remove any residual image material on the surface prior to a subsequent reproduction cycle. It is clear that other modes of charging, exposing, transfer or fusing may be utilized in connection with the present invention.

Referring now to FIGS. 2 and 3, there is illustrated one embodiment of the development device 10 of FIG. 1 according to the present invention. In particular, in FIGS. 2 and 3 a housing 11 is mounted by suitable means adjacent drum 1 and the housing includes an open side confronting the surface thereof. The housing 11 includes sealing means 12 to contact the drum surface and prevent loss of developer material therebetween. A channel underplate 13 is positioned within the housing wherein the underplate is curved to approximately conform to the curvature of the drum. A series of parallel channel members 14 in the form of vanes are fixedly mounted on the channel underplate 13 and non-perpendicularly extend therefrom to create a series of developer flow channels. The channel members 14 extend parallel to the drum surface in the direction of movement thereof and are shaped with a curvature or are form to allow a given point on the latent image of the drum to pass a plurality of channel members. Any number of channel members may be utilized on the underplate depending on the number of developer material channels desired for selected development results. The underplate and channel members are electrically grounded to act as a development electrode to improve development of solid image areas or alternatively, may be connected to a suitable electrical potential (not shown) to also aid in preventing background or non-image deposition of the toner.

The underplate 13 is supported by a pair of shafts 15 which extend through openings 16 in the housing 11 to a respective magnetic core 17 wherein each shaft is connected to a coil 18 which surrounds an arm of the respective core. The two cores 17 are connected to a suitable alternating electrical potential (not shown) to reciprocate the two shafts in unison and oscillate the underplate and channel members in a different parallel to the axis of rotation of the drum. However, it is within the scope of the present invention to use other conventional oscillating means instead of the coil and magnetic core device as disclosed herein if desired.

A plurality of flat inner vanes 20 are secured together as a unit by a suitable connecting frame means 21 1ocated at each end of the vanes. The plurality of inner vanes are shaped along their length to conform to the curvature of the channel member wherein a single inner vane extends within two respective channel members 14 in an interlaced form. A vane 20 extends within each flow channel created by two adjacent channel members 14 whereby the plane of the surface of the vane intersects the plane of the surface of the channel members so that an angular relation exists therebetween. The flat surface of vane 20 is described for convenience of illustration as extending diametrically from the drum, although other angular orientations may be utilized. The plurality of inner vanes 20 are supported as a unit within their respective channel members by two shafts 22 mounted to a bracket connected to the inner vanes and extend through openings 23 in the housing 11 to a suitable driving means. The driving means of the vanes 20 is similar to the driving means disclosed herein for the underplate and includes an E-shaped magnetic core 24 which effects reciprocation of the shaft 22 through a coil 25 mounted thereto. An electrical potential (not shown) alternately energizes the coil 25 to cause an oscillating movement of the vane means as a unit. The oscillating movement of the vanes 20 is preferable out of phase with the motion produced on the underplate whereby the vanes and channel members 14 move in opposite directions and require only one-half of the amplitude required if either the vane or channel member were to remain stationary. However, it is within the scope of the present invention to oscillate only the underplate with respect to the inner vane or vice versa if such relative motion were desired. Further, the vanes 20 also may be utilized as development elec trode by being electrically grounded or being connected to an electrical potential (not shown).

The relative motion of the inner vane 20 with respect to the adjacent channel members 14 effects a circulation of developer around the inner vane. Such a circulation of material around the inner vane occurs because as the vane moves against an adjacent channel member, the orientation of the channel member causes a movement of developer material in a first direction along the inner vane. Then as the vane and channel member move in the opposite direction, the developer material is given an opposite movement as clearly illustrated in FIG. 4 where the developer flow is indicated by the arrows. It should be apparent, therefore, that the relative movement of the inner vane with respect to the channel members causes a circulation of developer material around the inner vanes 20.

Referring again to FIGS. 2 and 3, developer material is introduced into the channel members at the top portion 26 thereof and developer material flows along each of the flow channels through the effect of the movement of the drum surface and gravity. As the channel members 14 and the inner vanes 20 are oscilalted relative to each other, the developer circulates around the inner vane in each flow channel and accordingly traverses the development zone in a helical motion. The developer helically flows through each of the flow channels and reaches the bottom end 27 thereof to be recirculated back to the top of the development device. A developer conveying device 30 is mounted within the housing 11 beneath the channel underplate 13 to lift the developer to the top portion 26 and may comprise, for example, an anger means or other suitable means.

The circulation of developer material in a helical motion along the inner vanes 20 of the channels in the development zone provides a high degree of mobility of the developer along the drum surface and reduces the coupling of the carrier particles to the drum. Since adequately tonerized carrier particles are constantly agitated to a high degree in the development zone and are, therefore, adequately circulated in the present invention, the leading edge of solid image areas are most efficiently developed as compared to prior art development systems. Further, it should be apparent that the helical motion 7 of developer around the inner vanes improves overall development of the latent image since all the developer traveling through the development zone is in development contact with the image to prevent any localized carrier particles becoming depleted of toner.

Referring to FIG. 5, there is illustrated another embodiment of the development device 10 according to the present invention. A developing housing 40 is mounted beneath the photoconductor drum and includes an open side 41 wherein the top of the housing overlaps the bottom surface of the photoconductor drum 1. The development device of FIG. circulates developer about an inner vane member based on the same principle as the embodiment herein disclosed in the description of FIG. 2. However, the vane members 42 in the embodiment of FIG. 5 extend across the drum surface instead of substantially along the direction of movement of the drum surface as the form of FIG. 2. The vane members 42 of FIG. 5 are movable within channels formed by a stationary plastic screen having a base body 45 cured to conform to the shape of the drum surface in direct confrontation to the surface thereof. The stationary plastic screen further includes a series of screen members 46 extending therefrom in substantially radial direction to the drum 1 to form a circulating compartment 47 for the developer material. Each of the vane members 42 are positioned within a respective compartment 47 and the vanes 42 are secured together by a securing means (not shown) to move as a unit in the circulating compartments. The vane members 42 are angularly disposed in each compartment to effect movement of the developer when oscillated therein.

The vane members are connected to a suitable oscillating device (not shown) suitably mounted on the exterior of the housing wherein the vanes are moved by the oscillating means as a unitary member. Accordingly, the movement of the vane member 42 against the adjacent screen member 46 compresses the developer to force the material therebetween to move in one direction and as the vane is oscillated against the other adjacent screen member, the developer material is moved in an opposite direction to create an orbiting developer flow around each of the vane members 42. The orbiting developer material is introduced through the screen base body 45 into the development zone adjacent the drum to develop the electrostatic image thereon.

The screen members are open at the bottom thereof to communicate with a developer sump 50 which retains a supply of developer material of sufficient quantity to contact the bottom of the vane members 42. Toner is supplied to the developer sump by means of a pair of angers 51 from a supply of toner whereupon excess toner is introduced into the developer sump. The excess toner will readily attach to carrier particles circulating around the electrode vane 42 and, therefore, as the carrier moves up one side of the vane 42 from the sump 50, they carry an excess amount of toner. The excess toner on the carrier moving up to the developing zone is removed by electrodes 52 connected to a suitable potential, and the electrodes 52 are mounted on respective vane members 42 and are insulated therefrom by electrically insulating material 53. The electrodes 52 create an electric field across an adjacent screen member 46 to the vane member located in the adjoining flow compartment 47. The magnitude of the field created by the electrode 52 is selected to cause excess toner to be removed from the carrier through the screen member 46 as the developer moves up to the developing zone to insure that optimumly tonerized carrier contacts the drum surface.

Further, the oscillating vane member 42 may be connected to a suitable potential (not shown) or may be electrically grounded to act as a development electrode in a well-known manner to produce satisfactory solid area development and prevent deposition of toner to nonimage background areas of the drum. Therefore, the embodiment of FIG. 5 creates a highly mobile circulation of development material around the angularly disposed vane members whereupon the carrier is delivered into the development zone through the base body of the screen in an optimumly tonerized state to improve development of the image thereon. Further, the highly mobile character of the circulation of the development material around the vane 42 prevents the masking or adherence of developer material along the image bearing surface thereby adequately developing the leading edge of solid area.

In the above description there has been disclosed an improved apparatus for effectively developing a latent electrostatic image supported on a xerographic photosensitive surface. The surface to be developed was described for convenience of illustration as being that of a xerographic drum, but the invention may be used to develop other well-known photosensitive members in the form of plates, belts, Webs, or coated papers. Further, it is Within the scope of the present invention to utilize other shapes, curvatures, or orientations of the interlaced vane and channel members than as disclosed herein depending on the desired degree of developer circulation, the shape or form of the utilized photosensitive surface and the like. Further, the embodiment of FIG. 2 disclosed herein may be horizontally oriented to create the desired helical flow wherein the motion of the surface bearing an image to be developed produces the longitudinal movement of the flow.

While the invention has been described in reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof Without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from is essential teaching.

What is claimed is:

1. An apparatus for developing a support surface bearing a latent electrostatic image with developer material comprising:

a vane means angularly positioned between two channel members, both vane means and channel members extending substantially parallel to the image bearing surface to be developed; and

circulating means to create a helical flow of developer material about the vane means.

2. The apparaus of claim ll further including means to oscillate the vane means relative to the two channel members to create a circulating flow of developer material about the vane means within the two channel members.

3. The apparatus of claim 2 further including means to effect movement of the developer material along the axis of the vane means during circulation thereabout to create said helical flow of developer material.

4. The apparatus of claim 3 wherein said vane means is a development electrode.

5. The apparatus of claim 3 further including means to move the image bearing surface to be developed relative to the vane means.

6. The apparatus of claim 5 wherein said vane means extends in a skewed direction with respect to the direction of movement of the image bearing surface.

7. An apparatus for developing a support surface bearing a latent electrostatic image with developer material comprising:

a vane means angularly positioned between two channel members, both vane means and channel members extending substantially parallel to the image bearing surface to be developed; and

circulating means to orbit developer material about the elongated vane to elfect contact of the developer material with electrostatic image to be developed.

8. The apparatus of claim 7 wherein said circulating means includes means to oscillate the elongated vane means Within a channel means.

9. The apparatus of claim 8 wherein said vane means is oscillated in contact with a sump means supporting developer material to supply developer material for orbiting about said vane means.

References Cited UNITED STATES PATENTS 3,081,737 3/1963 Frantz et a1 117-17.5 X 3,357,399 12/1967 Fisher 118-637 'S-wyler 1 18-6-37 Donalies l17-17.5

Donalies 1 18-637 Knechtel 1 18637 Gundlach 11717.5 Smelling 1 18637 Lace 118-637 Hagenbach 11717.5

US. Cl. X.R. 

